Vision systems that perform measurement, inspection, alignment of objects and/or decoding of symbology (e.g. bar codes) are used in a wide range of applications and industries. These systems are based around the use of an image sensor, which acquires images (typically grayscale or color, and in one, two or three dimensions) of the subject or object, and processes these acquired images using an on-board or remote, interconnected vision system processor. The processor generally includes both processing hardware and non-transitory computer-readable program instructions that perform one or more vision system processes to generate a desired output based upon the image's processed information. This image information is typically provided within an array of image pixels each having various colors and/or intensities. In the example of a symbology (barcode) reader, the user or automated process acquires an image of an object that is believed to contain one or more barcodes. The image is processed to identify barcode features, which are then decoded by a decoding process and/or processor obtain the inherent alphanumeric data represented by the code. In other types of vision systems, various vision system tools (e.g. edge detectors, calipers, blob analysis) are employed by the system processor to detect edges and other features that allow for recognition of object features, and the determination of desired information based upon these features—for example whether the object is defective or whether it is properly aligned.
In a vision system, a key component is the vision system camera assembly. The camera assembly includes a lens (optics) and an imager (or “sensor”) that provides the array of image pixel information. The vision system processor, as described above, receives the pixel data from the imager/sensor and processes it to derive useful vision system information about the imaged scene and/or object. The vision system processor and related components (e.g. data memory, decoders, etc.) can be provided within the camera assembly's housing or enclosure, or some or all of these components can be mounted remotely (e.g. within a PC, or other remote, self-contained processing system), and linked by a wired or wireless interconnect. Likewise, the camera assembly can include an on-board (internal) illuminator that typically surrounds the lens, and/or another illumination arrangement that provides light to the imaged scene.
In some vision system cameras, it is desirable to provide an automatic focus (“auto-focus”) capability. Many auto-focus arrangements rely upon electromechanical actuation to move a fixed lens, while others increasingly rely upon other forms of varioptic lens designs, such as a so-called liquid-lens.
In the particular field of symbology reading using sensor-based vision systems, a common reader arrangement employs a handheld unit that is directed at an object containing a symbol (e.g. a 1D or 2D barcode). Such handheld systems are commonly employed to track inventory, for example in a warehouse or factory floor. In such environments, the distance between a symbol and the reader can be highly variable, as some objects can reside relatively close to a user, while others are disposed at a distance (e.g. an object located on a high shelf). While a ready may include a conventional auto-focus mechanism to allow it to generate a sharp image of both the close object and the far object, the symbol in the far object can appear small relative to the overall field of view given this long focal distance as the opening angle of the optics is too large. As such, the small size of the symbol in the overall image may render it difficult to properly decode due to lack of sufficient resolution when compared to the overall field that is captured by the sensor (i.e. the feature of interest/symbol is too small at distance).
It is therefore desirable to provide a vision system camera assembly that can more effectively resolve a symbol or other feature of interest at both short focal distances and long focal distance. This camera assembly should be adaptable to a handheld device and/or to a fixed-mount device.